Prior processes for forming the humidity-sensitive membrane generally use dipping, spin coating, spraying and dispenser spreading methods, and as the base material various materials including hard base materials such as alumina or epoxy, and soft base materials such as polyimides have been used depending on the purpose of use.
The dipping method is a method which comprises attaching lead wire to the base material onto which the electrode is formed, followed by fixing to a jig, dipping vertically to the humidity-sensitive membrane for a certain period, then raising to make level, drying and then thermally reacting to form the humidity-sensitive membrane.
The spin coating method is a method which has been frequently used in semiconductor procedures, and forms the humidity-sensitive membrane onto electrodes by dropping polyelectrolyte solution onto the rotating electrodes.
The spray method is a method which forms the humidity-sensitive membrane by spraying polyelectrolyte solution through nozzle to spread onto the electrodes.
The dispenser spreading method is a method which forms the humidity-sensitive membrane onto electrodes by injecting polyelectrolyte solution in several microliter units via a microinjector.
At the present time, although the above methods have been widely used, they have disadvantages including complicated procedures, relatively long process times, a loss of raw materials, low yields and high expenses. Particularly, since it is very difficult to from the humidity-sensitive membrane having a certain thickness in the state that the electrode has already been formed in a substantial thickness, it is very difficult to control the properties required to have accuracy. Further, the dipping method as a most widely used method can be readily applied to the hard base materials but has a great difficulty in spreading the humidity-sensitive membrane onto the soft base materials.